How much difference does a phono stage make?

The phono stage is the weak link in most analogue chains. Get the best you can stretch to afford.

Agree with all the above.

I've owned $150 cartridges and $5,000 cartridges. I also own an $1,800 preamp and a $12,000 one. Like Syntax, if I had to pair the lesser of one with the greater of the other - and could only keep one combo - I'd keep the good preamp + a cheap cartridge, not the cheap preamp + a good cartridge.

The same is true of turntables and tonearms vs. cartridges. If I had to choose between my $1K rig + a $5K cartridge or my $11K rig + a $150 cartridge, I'd choose the latter every time. $150 cartridges play better than you'd think possible on a good rig. $5K cartridges on a cheap rig just reveal its flaws and shortcomings.

In general, the expenditure or upgrade order should be:
1. phono stage
2. turntable
3. tonearm
4. cartridge

In your case, your next upgrade after the phono stage should be speed control for the Scout, which will also make a nice improvement.

The PH-3 is a very good phono preamp. It is an older model(not the lowest end model) It was at one point ARC's top of the line model.(model years 1995-1998) You will notice a significant difference in performance from what you have now!
For those who don't know, the line of progression of ARC phono preamps: PH-1 and the Reference models: Reference 1
PH-2 Reference model 2
PH-3
PH-3Se
PH-5
PH-7

Totally agree w all posters above.

Look for the PH3SE, it is worth the $150 more difference. I had the PH3 and then the PH3SE. Plenty of difference. Great value. The 5 and 7 are also good but not good values.